The present invention relates to a visible radiation semiconductor light emitting device using InGaAlP based compound semiconductor material and used in a display panel or an LED panel. More specifically, the invention relates to a semiconductor light emitting device capable of reducing mechanical deficiencies such as a fracture or a crack of a light emitting chip at the time of handling such as assembling of the semiconductor light emitting chip into a lamp.
As shown in FIG. 4, a conventional visible radiation lamp-type semiconductor light emitting device is formed such that a semiconductor light emitting chip (LED chip, hereinafter) 20 is mounted in a recess in a tip end of one lead 31, a wire bonding is established with the other lead 32 by a metal wire 33 so that both electrodes 27 and 28 of the LED chip-20 are electrically connected to the two leads 31 and 32, the connected portions are coated with transparent epoxy resin, and thereby a package 35 is provided.
This LED chip 20 is formed in the following manner. That is, a light emitting layer forming portion 29 having a double hetero junction structure in which an active layer made of non-doped InGaAlP based semiconductor material is sandwiched between an n-type clad layer and a p-type clad layer both made of InGaAlP based semiconductor material. The active layer has such a composition that a band gap energy thereof is smaller than those of the clad layers. A p-type current dispersion layer. 25 comprising AlGaAs is sequentially formed on a surface of the light emitting layer portion 29 by epitaxial growth. A p-side electrode 27 is provided on a surface of the current dispersion layer 25 by means of Auxe2x80x94Gexe2x80x94Ni alloy or the like through a contact layer 26 made of p-type GaAs, an n-side electrode 28 is provided on a back surface of a semiconductor substrate 21 by means of Auxe2x80x94Gexe2x80x94Ni alloy or the like, and a wafer is divided into chips.
Conventionally, this kind of semiconductor light emitting device requires, working to divide a semiconductor wafer into chips to mount each chip 20 on a tip end of the lead 31, and to connect between the upper p-side electrode 27 and the second lead 32 by wire bonding. Therefore, at the time of chipping and handling for mounting the chip, or at the time of wire bonding, a force is partially applied to the LED chip 20, and a fracture or a crack is generated occasionally Since this LED chip itself is as small as 0.3 mmxc3x970.3 mm, if a fracture or a crack is generated even partially, there is a problem that brightness is largely lowered and the chip becomes faulty.
The same problem is caused not only when an LED chip is bonded to a tip end of a lead to produce a lamp-type light emitting device, but also when an LED chip is directly bonded on a substrate, and when an LED chip is die bonded on an insulated substrate and is coated with resin flatly to form a chip-type light emitting device.
The present invention has been accomplished to solve the above problems, and it is an object of the invention to provide a semiconductor light emitting device capable of enhancing yield of assembling procedure without causing a fracture or a crack in an LED chip at the time of handling for mounting or wire bonding.
In order to reduce a possibility of causing a fracture or a crack in an LED chip at the time of handling for mounting or wire bonding, the present inventors earnestly studied and as a result, it was found that by allowing an AlGaAs layer which is the uppermost semiconductor layer exposing at a surface of the chip to grow at a high temperature, e.g., about 720xc2x0 C., its hardness is largely increased, and by increasing the hardness of the outermost semiconductor layer, it is possible to largely reduce a possibility of causing a fracture or a crack in the chip at the time of handling.
A semiconductor light emitting device of the present invention comprises a semiconductor substrate, a semiconductor lamination portion having a light emitting layer forming portion made of InGaAlP based compound semiconductor and a current dispersion layer made of AlGaAs based compound semiconductor, and two electrodes, one of them being provided on a portion of a surface of the semiconductor lamination layer portion and the other one being provided at the. side of a back surface of the semiconductor substrate, wherein Vickers"" hardness of a semiconductor layer exposed on at least the outermost surface of the semiconductor lamination portion is 700 or higher.
Here, InGaAlP based compound semiconductor is represented in a form of In0.49(Ga1xe2x88x92xAlx)0.051P, and the value of x is variously changed between 0 and 1. Meanwhile, 0.49 and 0.51 which are mixed crystal ratio of In and (Al,Ga1xe2x88x92x) mean ratio of lattice alignment with a semiconductor substrate such as GaAs on which InGaAlP based material is laminated. AlGaAs based compound semiconductor means a compound semiconductor whose mixed crystal ratio between Al and Ga can be varied.
When the semiconductor lamination portion comprises a light emitting layer forming portion and a current dispersion layer, Vickers"" hardness of the current dispersion layer may be 700 or higher. Further, when the semiconductor lamination portion comprises the light emitting layer forming portion, the current dispersion layer and a protecting layer made of AlGaAs based compound semiconductor, Vickers"" hardness of the protecting layer may be 700 or higher.
A contact layer may be interposed between the current dispersion layer and the one electrode.
If a carrier concentration of the current dispersion layer is 1xc3x971018 to 5xc3x971019 cmxe2x88x923, current dispersion effect is enhanced.
It is preferable that the light emitting layer forming portion and the current dispersion layer are laminated by MOCVD method, and the current dispersion layer and/or the protecting layer is allowed to grow at a temperature higher than that of the light emitting layer forming portion, because it is easy to form the semiconductor layer with the above-described hardness at high carrier concentration.
If the semiconductor substrate is formed into n-type and the current dispersion layer is formed into p-type,and a dopant of the current dispersion layer is Zn it is easy to obtain high carrier concentration and to increase the hardness.
For example, the current dispersion layer comprises AlyGa1xe2x88x92yAs (0.5xe2x89xa6yxe2x89xa60.8), and the protecting layer comprises AlzGa1xe2x88x92zAs (0.3xe2x89xa6zxe2x89xa60.6).